“[PRISM] is an incredibly powerful and invasive tool,”
Greenwald told ABC’s ‘This Week.’ The NSA programs are
“exactly the type that Mr. Snowden described. NSA officials
are going to be testifying before the Senate on Wednesday, and I
defy them to deny that these programs work exactly as I’ve
said.”

The NSA keeps trillions of telephone calls and emails in their
databases which they can access anytime with simple screen
programs, he said.

“And what these programs are, are very simple screens, like
the ones that supermarket clerks or shipping and receiving clerks
use, where all an analyst has to do is enter an email address or
an IP address, and it does two things.”

“It searches that database and lets them listen to the calls
or read the emails of everything that the NSA has stored, or look
at the browsing histories or Google search terms that you’ve
entered, and it also alerts them to any further activity that
people connected to that email address or that IP address do in
the future.”

While the program conducts wiretapping with little court approval
or supervision, there are “legal constraints” on
surveillance that require approval by the Foreign Intelligence
Surveillance Act (FISA) of 1978, in which court judges can
secretly review the government's plans to track suspected
terrorists in advance.

Greenwald will testify before a Congressional committee on
Wednesday, along with NSA officials who have previously downplayed Snowden’s claims about the agency’s
easy-access data.

PRISM is a mass electronic surveillance data mining program
operated by the NSA since 2007. The program was exposed by former
NSA contractor Edward Snowden earlier this summer. Snowden leaked
information about the program to the media, warning of a far
greater extent of mass data collection than the public knew
existed. The disclosures were published by The Guardian and The
Washington Post on June 6.

Snowden later leaked further information to Greenwald which
pertained to mass security operations carried out across the
world. He spoke of British spy agency GCHQ, which uses the
Tempora surveillance program. The whistleblower also shared
information regarding Germany’s cooperation with US intelligence,
which reportedly combs through half a billion German phone calls,
emails, and text messages on a daily basis.

A call for transparency on surveillance programs

The call for increased oversight and transparency for
surveillance programs has been growing, even among supporters of
the NSA.

“I do think that we’re going to have to make some change to
make things more transparent,” Senator Saxby Chambliss, vice
chairman of the Senate Intelligence Committee, told ABC.

Former federal judge James Robertson, who used to grant
surveillance orders, said he was shocked to hear of changes to
allow broader authorization of NSA programs - such as the
monitoring of US phone records. He urged for a reform which would
to allow counter-arguments to be heard.

“What FISA does is not adjudication, but approval,”
Robertson said, speaking as a witness during the first public
hearings into the Snowden revelations. “This works just fine
when it deals with individual applications for warrants, but the
2008 amendment has turned the FISA court into an administrative
agency making rules for others to follow.”

However, government officials have defended the surveillance
initiatives as authorized under law, claiming they are necessary
in order to guard the country against terrorist threats.

Following Snowden’s revelations on NSA surveillance, President
Barack Obama assured US citizens in June that “nobody is
listening to [their] telephone calls."

He said the surveillance programs monitor phone numbers and the
durations of calls, adding that if there are any suspicions and
"if the intelligence community then actually wants to listen
to a phone call, they've got to go back to a federal judge, just
like they would in a criminal investigation."

President Obama added that America is "going to have to make
some choices" between privacy and security, warning that the
highly publicized programs will make it harder to target
terrorists.

Meanwhile, deputy FBI Director Sean Joyce said that the
“program is not intentionally used to target any US
citizens" and is “key in our counter-terrorism
efforts."

Testifying on Capitol Hill before the House Permanent Select
Committee on Intelligence in June, NSA director Gen. Keith
Alexander claimed that the NSA’s storage of millions of phone
records has thwarted more than 50 terror attacks in more than 20
countries since September 11, 2001. However, evidence of the
prevented attacks has not been revealed